Fluorescence neodymium laser

Fluorescence depolarisation by energy transfer (rather than rotational relaxation) between donor molecules of the same type can occur. Eisenthal [174] excited solutions of rhodamine 6G (9 mmol dm-3) in glycerol with 530 nm light from a frequency-doubled neodymium laser. The polarisation... 

Russian workers have also studied the potential for liquid homogeneous piunping in cortsiderable detail, by measuring the optical effects of adding urarttum compounds to liquid neodymium laser media, and the fluorescence efficiency of liqitid laser media excited by fission fragments. However, reactor-pumped lasing in these liquid media has not yet been repotted. 

Figure 8.7. Delayed fluorescence and diffuse reflectance transient absorption spectroscopy on scattering substrates. Example terthicnyl on silica gel excited with = 354 nm (neodymium/yttrium-aluminum-garnet) (Nd/YAG) laser pulse of 10 nsec, 20 mj), recorded with a gated diode array spectrometer.

The fluorescence lifetime, r, of Nd + in Ca3Ga2Ge30i2 crystal (a solid state laser) is measured as a function of the neodymium concentration, Cnij, giving... 

Nassau 110) has published the concentration dependence of the fluorescent lifetime of neodymium in CaW04 Nd3+ Na+. All studies were made on very high-quality laser crystals. The neodymium concentration varied from 0.1 to 5.5 atomic per cent the charge compensating sodium was held fixed at 12 atomic per cent. All data were collected at 77°K. 

Hoskins and Soffer (117) measured the fluorescent lifetime of the neodymium 4Fy2 state in yttrium oxide. They found a value of approximately 260 /zsec both at room temperature and at liquid-nitrogen temperature. They also observed a weaker long-lived component in the decay. They were unable to say whether this was evidence for a low-transition-probability ion site, or an effect of trapping of the resonance radiation near 0.9 /x. They report laser action, with a threshold of 260joules. This is a fairly high value for most crystalline materials. 

Geusic et al. (118) made measurements of the fluorescent lifetime of neodymium in yttrium aluminum garnet (Y3A15012). For neodymium concentrations up to 3 atomic per cent, the measured fluorescent-decay time is approximately 200 jtxsec at both IT and 300°K. Above 6 atomic per cent, a marked decrease in the fluorescent lifetime is observed. They suggest that this is due to neodymium interactions. It is to be noted that yttrium aluminum garnet is a laser material of very exceptional quality. 

To a very large extent, most of the recent data on fluorescent decay times of the other trivalent ions (those beside terbium, neodymium, and europium) stems in some way from laser experiments. In this section some representative data on these are considered. 

A neodymium-ytterbium-coupled rare-earth ion system was given extensive study by Peterson and Bridenbaugh (109, 166) Peterson et al. (167) and Pearson and Porto (168). The simultaneous doping of Nao.5Gdo.5-W04, or Calibo (168) glass with neodymium and ytterbium results in a resonance-coupled system in which energy pumped into the neodymium appears as fluorescence from the ytterbium. The fact that the energy absorbed by the neodymium is rather efficiently transferred to the ytterbium results in a substantial reduction in laser threshold for ytterbium. 

Many aryl-substituted pyrylium salts are intensely fluorescent. It is possible to predict these spectral properties by a consideration of the shape of the molecule, the nature of substituents and the length of the ir-electron system (75MI22203). Pyrylium salts have been used as Q-switches for neodymium and ruby lasers in acetonitrile (68MI22200). 

The quantum yields of fluorescence of the different systems have also been determined relative to a single crystal of neodymium-doped YAG for which a quantum yield of unity has been assumed (Heller, 1968a). The quantum yields obtained, even if they are accurate only within a factor of two, follow the same trend as for the lifetimes, with the highest values for the acidic solutions 0.70 and >0.75 in presence of S11CI4 and SbCls, respectively. Neutral and basic solutions are less luminescent and have quantum yields of 0.5 and 0.4, respectively. Identical measurements performed on a sodium-compensated neodymium-doped calcium tungstate crystal lead to a value of 0.5. The high quantum efficiency and the low threshold (between 2 and 40 J) of these Nd3+ SeOCl2 systems clearly demonstrate that liquids are not inherently inferior to solids as laser materials. 

Many real-world samples fluoresce when iUuminated with visible light, especially green light from a frequency-doubled neodymium-doped yttrium aluminum garnet (Nd-YAG) laser at 532nm or from an argon ion laser at 488 or 514.5nm. 

In metabolic cytometry, cells are incubated with a substrate that is tagged with a highly fluorescent dye we prefer tetramethylrhodamine because of its excellent spectroscopic properties and its compatibility with the frequency-doubled neodymium YAG laser. This substrate is prepared at high concentration and undergoes chromatographic purification to eliminate fluorescent impurities. 

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